Method of leaching copper ores.



JAMES w. iiE'IL'L, OF SALT LAKE CITY, UTAH".

Merl-ion 0F LEACHlNCt coprri oas s.

SPECIFICATION forming part a Letters Patentfi'o. 650,784, dated May 29, 1960.

Application filed September 29, 1899 To all whom it may concern: r

Be it known that 1, JAMES W. NEILL, a citizen of the United States, residing at Salt Lake City, in the county of Salt Lake and State of Utah, have invented certain new and useful Improvements in Methods of Leaching and,

Extracting Copper Ores; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention relates to the extractionof copper from ores or failings of copper ores or scribed more particularly in its application to ores of that character.

The object of the process, as usual in the art, is to finally obtain the copper contained in the ore in a metallic state, or as cupric oxid, or as cuprous snlfid, or in other commercial form; but the main or principal features of the process which constitute my invention are, briefly, first, the subjection of the ores (either with or without previous roasting of the same, depending upon the character of the ore) to the action of sulfurous acid (as gas or in solution) to dissolve out the copper, and, second, the heating of the solution thus obtained to drive off the excess of sulfurous acid and form a copper precipitate, which may be subjected to any desired after treatment or not, as may be required. I

In the case of sulfid-of-copper ores or other ores containing sulfur as a constituent the roasting of the ore has the incidental advantags that it affords as a by-product the'sulf urous acid employed in my process. In other cases the sulfurous acid may be obtained from the direct burning of sulfur or in other ways, as well understood in the art. I am aware that sulfuric acid has been very commonly employed in the extracting of copper Serial No. 732,111. (No specimens.)

from its ores; but the advantages in the use of sulfurous acid are very many. Sulfuric acid can seldom be bought in localities where copper ores abound at less than two cents per pound, and insuc'h localities roast fumes f. are usually abundant, and my solvent sulfurous acid would practically cost nothing; but were there no froast fumes or gasesi and if it were necessary to use sulfur instead 1 my method of treatment. of ores or tailin 's above referred to, is still much cheaper. n places where sulfuric acid can be bought for two cents per pound s'ulfur can also be bought for two cents per pound. It takes ninetyeight pounds of sulfuric acid to dissolve sixty-three pounds of copper, while itonly takes thirty-two pounds of sulfur in the forni of sulfurous acid to dissolve the same amount of copper sixty-th'ree pounds. Therefore my method in this case is three times as cheap in the cost of material used in treating material and ores, above referred to, containing copper, as compared with sulfuric acid; but the advantage flowing from the use of sulfurous acid does not stop there. It (sulfurous acid) being a much weaker acid than sulfuric acid, does not attack so vigorously the other metallic contents contained in the ores or material treated, thus fouling the solution and wasting the acid. ous acid) attack the vessels or implements of the plants to the same extent as the stronger acid (sulfuric) would do, and for the same reason it is much easier and cheaper to reduce the copper obtained from the ores and tailings after treatment with sulfurous acid than it would be to reduce the copper obtained by sulfuric acid, either by using the electric current or scrap-iron.

Neither does it (sulfur The sulfurous acid as employed in my process may be used either as a gas (as will be presently described) or in solution, or both,

but preferably the sulfur contents of the ore, tailings, or material after the roasting should contain sulfur below one per cent., (1%.) Then and in that case the copper is entirely soluble in sulfurous acid, and my process is thus best carried out. The ore is now ready to be subjected to the action of sulfurous acid, (as gas is in solution,) which constitutes the first step of my improved process. This may be accomplished by placing the crushed and roasted ores Mankspnvats, preferably of wood and of a sizeand shape adapted to special or local conditions. These vats or tanks may be supplied with stirring-arms or other devices by which to agitate the contents, and thus hold the ores in a state of suspension, or the vats may be only supplied with false bottoms and filtering-cloth. In these vats the ore is subjected to the action of sulfurous-acid solution or of sulfurous-acid gas, or both, direct, and the ores may be'kept in a state of suspension, if desired or necessary, or may be allowed to remain in place in the tanks or vats, and the solution or gas may then be percolated through the mass of the ore. As soon as the copper is dissolved by the solution or the gas, and this may be easily determined by taking a small sample from the tank or vat and testing it in the usual manner for copper, the solution is then withdrawn from the ore either by filtration, allowing the previously agitated mass to settle, then decanting the solution,or by other means, and this solution I pass to other vats forfurther manipulation. The ore is then preferably given a washing with pure water or water containing a small amount of sulfurous acid inorder to remove any of the solution carrying the copper, and so clean out the ore and leave it in a condition where it may be taken from the tanks or vats and thrown on a dump as a waste. This washwater may be saved and used in the apparatus for collecting and making the solution of sulfurous acid and reused as a solvent on the ore, thus making a saving of water in districts'where the same is scarce. The solution of sulfurous acid containing copper, as cnprous sulfite, held in solution therein by the excess of sulfurous-aeid gas, isnow subjected to the second step of my improved process, which consists in heating the solution to a temperature sulficient to drive out the excess of sult'urous acid, thereby precipitating the copper in the form of a bright-red and very heavy powder, (cnprous sulfite.) This cnprous suliite settles at once to the bottom of the tank or vat, and the remaining solution may be readily and entirely siphoned or decanted from it, or the cnprous sulfite may be recovered from the solution by filtration. To effect the heating or boiling of the solution, waste or exhaust steam may be used while the solution is contained in wooden tanks or vats, thus making it a very cheap method of extracting copper from the solution. The excess of sulfurous-acid gas thus driven out of the solution may be carried to the apparatus and again absorbed in water, thus preventing any losses or escape of gas. The cnprous sulfite after it has been removed from the tanks or vats, filtered, and dried contains about fifty per cent. of metallic copper, and it may be heated in an oxidizing atmosphere in a furnace and the cupric oxid produced, which is useful in commerce and may be sold as such, or it may be melted in afurnace in a reducing atmosphere, producing cnprous sulfid, which may then be reduced to metallic copper in the process known as the Bessemer process, for which this material would be perfectly fitted.

Should the oxidation or roasting of the crude ore not have been perfect, some copper sulfate will remain in the ore and be taken up by the solution. In this case all the copper will. not be precipitated by boiling of the solution, and some will remain in the residual solution. This must be either passed over scrap-iron to regain this remaining portion of copper, or it may be passed through vats, Where it is subjected ,to the action of an electric current, which precipitates the copper.

The sulfurous acid used in the above process to dissolve the copper from the ore may, as already stated, be obtained from any desired source. Preferably I obtain it from the sulfid ore by collecting the fumes from the roastingfurnaces. These may be passed through water in some well-known and usual manner in a suitable apparatus, such as tanks or towers of wood or stones over which water is allowed to drip, the sulfurous-acid gas being absorbed by the water and this 11ydrated sulfurous acid so made being used as the solvent for dissolving copper from its ores or tailings. Itis very apparent that this sol vent thus made is a very cheap one and, furthermore, that the absorption of this harmful gas from the furnace-fumes must be a great benefit to a community around metallurgical works Where this gas is produced. In other cases or under other conditions the sulfurous acid (gas) obtained in the manner above stated or in any other manner may be applied to dissolve out the copper by passing it at once through vats containing the ores (oxids or carbonates) in a state of pulverization and wet, the ore suspended by continued agitation in the water, if so desired or expedient, or the gas may be caused to ascend through a mass of the wet ore, which dissolves the copper therefrom very rapidly, and the salt so formed is at once taken 'up by the water and held in solution.

My process may also be applied to ores in which the copper is present naturally in the form of an oxid of copper, as in cuprite, or when the copper is present in the form of a carbonite of copper, as in malachite or azurite. \Vhen the copper is present as sulfid chaleopyrite, chalcoeite, bornite, &c., the copper ore must first be converted into the form of etojs i a an oxid by roasting same, as hereinbefore described, and then dissolved from the ore by means of the sulfurous-acid gas or a solution of the gas or both.

In the foregoing specification and following claims the term ore is used as including tailings or other material or ore treated by roasting or otherwise previously to treatment by my process.

Having described my invention, What I claim, and desire to secure by Letters Patent, 1s-= 1. The herein described process of extracting copper from copper ores consisting in first dissolving out the copper by means of sulfurous acid and then heating the resultant solution to drive off the excess of sulfurous acid and precipitate the copper as and for the purpose described.

2; The process of treating and extracting copper from sulfid-of-copper ores, tailings or,

In testimony whereof I have hereunto affixed my signature in presence of two witnesses. i

JAMES WV. NEILL WVitnesses:

HENRY STERN, JAMES R. ROGERS. 

